Pressurized water is commonly used for cleaning solid surfaces. The use of extremely high pressure water (20,000 psi or more) for industrial cleaning is commonly known as waterblasting. FIG. 1 illustrates conventional waterblasting equipment. The equipment includes a hose A that carries high-pressure water from a high-pressure pump (not shown), a foot-operated valve B, and a lance C. The lance consists of a hollow metal rod D having a knurled handle E threaded onto its proximate end and a nozzle F with a small orifice threaded onto its distal end. Water exiting the lance is at such a high velocity that it can cause serious injury to person and property. Persons who conduct waterblasting wear heavy protective equipment, but can still be seriously injured if hit by a direct spray.
Tube-and-shell heat exchangers are widely used in industry. In a tube-and-shell heat exchanger, one fluid flows through the inside of multiple parallel metal tubes while another fluid at a different temperature flows outside the tubes. Heat is transferred from the hotter fluid to the cooler fluid as the fluids flow through the heat exchanger. Tube-and-shell heat exchangers are sometimes known as heaters, evaporators, coolers, condensers, etc. depending on the desired effect on the fluid of greatest economic importance.
Many industrial tube-and-shell heat exchangers are operated with fluids that cause deposits to form on the inside of the tubes. These deposits adversely affect the rate of heat transfer and, if substantial enough, can even affect flow rates. Periodic cleaning by waterblasting is commonly performed to remove these deposits.
FIG. 2 illustrates the cleaning of tubes G in a vertical heat exchanger H with conventional waterblasting equipment. A worker J wearing protective equipment holds the lance, inserts it into a tube, opens the food-operated valve, and then moves the lance up and down (or back and forth in a horizontal heat exchanger) along the tube to dislodge the deposits from the tube. When cleaning of the tube is completed, the foot-operated valve is closed, and the lance is removed. The lance is then inserted into another tube, the foot-operated valve is reopened, and another tube is cleaned.
This waterblasting procedure suffers from one very serious danger. If the worker performing the waterblasting accidentally withdraws the lance out of the tube without shutting off the valve (which can happen if the worker forgets to close the valve or if the worker is cleaning the portion of the tube near the proximate end and inadvertently withdraws the lance too far), the high velocity flow of the water against the edge of the tube causes the lance to be propelled backwards with a tremendous force. The lance can be dislodged from the grip of the worker and then whip about in an uncontrolled manner. If a worker is hit by the water flow or by the lance, serious injury or death can result.
Garman et al., U.S. Pat. No. 6,626,195, Sep. 30, 2003, discloses a waterblasting apparatus in which the lance is moved with a mechanical apparatus rather than manually. The apparatus is so large, heavy, cumbersome, and expensive that it is unsuitable for use in most situations. A number of safety cages, guards, and the like have been disclosed for various purposes. Examples include the devices disclosed in Childress, U.S. Pat. No. 3,910,359, Oct. 7, 1975; Molen et al., U.S. Pat. No. 4,381,027, Apr. 26, 1983; and Miller et al., U.S. Pat. No. 4,505,593, Mar. 19, 1985. However, these devices are not suited for use in waterblasting.
Accordingly, a demand exists for a way of eliminating the danger of an uncontrolled lance when manual waterblasting of a tube-and-shell heat exchanger is being conducted.